Mono is potentially no joke, it nearly killed my oldest daughter in the fall of 2009 when she was a senior in college. As it was, she missed a lot of classes.

Yes. From what I've read, the severity can vary from person-to-person and case-to-case. Federer was lucky as his was brief and not that severe. Soderling (and others) haven't been so lucky and it has turned into a prolonged struggle. It seems increasingly likely that it has ended his promising career prematurely. He was a guy, prior to his injury, who obviously had the potential with his talent and big game to catch lightning in a bottle a la Delpo in 2009 and steal a slam from the top guys.